A high recombination rate and high thermal budget for aluminum (Al) back surface field are found in the industrial p-type silicon solar cells. Direct metallization on lightly doped p-type silicon, however, exhibits a large Schottky barrier for the holes on the silicon surface because of Fermi-level pinning effect. As a result, low-temperature-deposited, dopant-free chromium trioxide (CrO , x< 3) with high stability and high performance is first applied in a p-type silicon solar cell as a hole-selective contact at the rear surface. By using 4 nm CrO between the p-type silicon and Ag, we achieve a reduction of the contact resistivity for the contact of Ag directly on p-type silicon. For further improvement, we utilize a CrO (2 nm)/Ag (30 nm)/CrO (2 nm) multilayer film on the contact between Ag and p-type crystalline silicon (c-Si) to achieve a lower contact resistance (40 mΩ·cm). The low-resistivity Ohmic contact is attributed to the high work function of the uniform CrO film and the depinning of the Fermi level of the SiO layer at the silicon interface. Implementing the advanced hole-selective contacts with CrO /Ag/CrO on the p-type silicon solar cell results in a power conversion efficiency of 20.3%, which is 0.1% higher than that of the cell utilizing 4 nm CrO . Compared with the commercialized p-type solar cell, the novel CrO-based hole-selective transport material opens up a new possibility for c-Si solar cells using high-efficiency, low-temperature, and dopant-free deposition techniques.

Dopant-free carrier-selective contacts are becoming increasingly attractive for application in silicon solar cells because of the depositions for their fabrication being simpler and occurring at lower temperatures. However, these contacts are limited by poor thermal and environmental stability. In this contribution, the use of the conductive high work function of cuprous iodide, with its characteristic thermal and ambient stability, has enabled a hole-selective contact for p-type silicon solar cells because of the large conduction band offset and small valence offset at the CuI/p-Si interface. The contact resistivity (≈30 mΩ•cm 2 ) of the Ag/CuI (20 nm)/p-Si contact after annealing to 200 °C represents the CuI-based hole-selective contact with low resistance and high thermal stability. Microscopic images and elemental mapping of the Ag/CuI/p-Si contact interface revealed that a nonuniform, continuous CuI layer separates the Ag electrode and p-type Si. Thermal treatment at 200 °C results in the intermixing of the Ag and CuI layers. As a result, the 200 °C thermal process improves the efficiency (20.7%) and stability of the p-Si solar cells featuring partial CuI hole-selective contact. Furthermore, the devices employing the CuI/Ag contact are thermally stable upon annealing to temperatures up to 350 °C. These results not only demonstrate the use of metal iodide instead of metal oxides as hole-selective contacts for efficient silicon solar cells but also have important implications regarding industrial feasibility and longevity for deployment in the field.

Cuprous oxide (Cu2O) is a nontoxic and earth‐abundant semiconductor material, which is a promising candidate for low‐cost photovoltaic applications. Although Cu2O‐based solar cells have been studied for a few decades, they still suffer from disappointing photovoltaic performance due to its high trap‐state density and inferior carrier collection efficiency. Herein, a facile solution method is demonstrated to synthesize high‐quality Cu2O films with low defects as hole transport layers (HTLs) and the Cu2O/Si heterojunction solar cells are fabricated. Moreover, a variety of interfacial engineering and light management strategies are adopted to push the efficiency limit of Cu2O/Si solar cells, including a Ag transparent conductive layer, HNO3 passivation, Mg electrode back contact, and MoOx antireflection layer, which enable the boosting of carrier separation and reduce the loss of incident solar light, yielding a record high power conversion efficiency of 9.54%. This work may pave the way for economical and environment‐friendly use of Cu2O/Si heterojunction solar cells in daily life.

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In order to compensate the insufficient conductance of heterojunction thin films, transparent conductive oxides (TCO) have been used for decades in both-sides contacted crystalline silicon heterojunction (SHJ) solar cells to provide lateral conduction for efficient carrier collection. In this work, we substitute the TCO layers by utilizing the lateral conduction of c-Si absorber, thereby enabling a TCO-free design. A series resistance of 0.32 Ωcm 2 and a fill factor of 80.7% were measured for a TCO-free back-junction SHJ solar cell with a conventional finger pitch of 1.8 mm, thereby proving that relying on lateral conduction in the c-Si bulk is compatible with low series resistances. Achieving high efficiencies in SHJ solar cells with TCO-free front contacts requires suppressing deterioration of the passivation quality induced by direct metal-a-Si:H contacts and in-diffusion of metal into the a-Si:H layer. We show that an ozone treatment at the a-Si:H/metal interface suppresses the metal diffusion and improves the passivation without increasing the